Loss of Arctic sea ice is linked to a decrease in polar bear birth rates in Canada's Hudson Bay, according to new research. If the trend continues, the polar bears in the region could be facing a population crisis.

In fact, if climate change continues unabated, the researchers say, polar bear populations across the entire Arctic will be in serious trouble.

Polar bears rely on sea ice during their hunting season, using the solid floes to reach waters rich with seals — polar bears' main food source.

Polar bear mothers retreat to a maternity den during pregnancy, never once emerging for food. An early spring ice breakup reduces the hunting season, and pregnant females aren't able to amass enough body fat to support them through their 8-month fast, when they must stay hidden in their dens to gestate their young and give birth.

Using mathematical modeling to estimate the impact of a shortened hunting season, the research team found that if ice in the Hudson Bay disappears one month earlier than in the 1990s, between 40 and 73 percent of pregnant female polar bears will not give birth to a surviving cub.

If the ice is gone a full two months earlier, between 55 and 100 percent of pregnant bears will not reproduce.